“That’s your opinion.”
For clarification, this statement, and ones similar to it, are often made after a person states an opinion in the midst of a heated argument.

For example:

“No, I think chunky monkey is a the stupidest ice cream on the planet. Strawberry is clearly the best. It’s simple. It’s classic. It’s known by all. Sometimes it contains actual strawberries. And you’re not left wondering if it’s made from actual monkey bits. Strawberry rocks.”

“That’s your opinion, monkey-face!”

One of the nice things about learning to distinguish between fact and opinion in elementary school is that this universal knowledge base mitigates the need to say “in my opinion” after stating an opinion.

So when I say that Mariano Rivera is the best closer in baseball history or that Sarah Palin would make a frightening President or that Ranch dressing is the most vile substance known to man, we all know that these are opinions, no matter how forcefully or with how much certainty I may state them.

Yes. It’s an opinion. We all know it’s an opinion. We know the difference between fact and opinion.

Just like it is an opinion when I tell you that you are a moron for defining my opinion as an opinion.

Distinguishing an opinion does not qualify as a valid verbal rebuttal.

In our world, we do not need to differentiate facts and opinions as we speak.